Long-term monitoring of sound exposure from shipping in coastal waters

Anthropogenic underwater noise from shipping is spatially and temporally pervasive throughout the world’s oceans, and has the potential to subject marine fauna to chronic noise exposure, the effects of which are poorly understood. Coastal waters are of particular concern due to the higher density of shipping activity and sensitive marine ecosystems (as well as potential waveguide effects). However, the high spatiotemporal variability of ambient noise in these regions presents a methodological challenge to long-term environmental assessment, which has previously focused on more acoustically stable deep-water observation sites. We present a method of characterising sound exposure from shipping using continuous passive acoustic monitoring combined with Automatic Identification System (AIS) shipping data. The method is applied to 9 days of data recorded in Falmouth Bay, UK, using a bottom-mounted autonomous recorder. An adaptive threshold is used to identify intermittent ship contributions to the 24-hr sound exposure level, and the spatial distribution of potential sources is analysed using AIS data. This indicates the spatiotemporal distribution of intermittent shipping noise sources, which can provide a more detailed understanding of anthropogenic noise in coastal waters and help to prioritise noise mitigation strategies in sensitive marine environments.